Inner spiral grooved tube with excellent heat transfer property and heat exchanger

ABSTRACT

An inner spiral grooved tube includes: a tube body; and grooves and fins aligned in an inner circumferential direction of the tube body, wherein the grooves and the fins are formed in a spiral along a longitudinal direction, an outer diameter is 3 mm or more and 10 mm or less, a number of the fins is 30 to 60, made of a metal, a cross sectional shape of each of the fins has a rectangular shape having an apex angle of 0±10°, a ratio h/f is 0.90 or more and 3.40 or less, h being a fin height and f being fin width, a ratio c/f is 0.50 or more and 3.80 or less, c being a fin spacing, and an average of the ratio h/f and the ratio c/f is 0.8 or more and 3.3 or less.

TECHNICAL FIELD

The present invention relates to an inner spiral grooved tube withexcellent heat transfer property and a heat exchanger.

Priority is claimed on Japanese Patent Application No. 2019-217340,filed Nov. 29, 2019, the content of which is incorporated herein byreference.

BACKGROUND ART

Conventionally, copper alloy tubes have been used for heat transfertubes in fin-and-tube type heat exchangers. However, due to thedepletion of copper resources, rising copper ingot prices, andrecyclability, aluminum alloy heat transfer tubes, which arelightweight, inexpensive, and highly recyclable, are beginning to beused.

In heat transfer tubes made of copper or an aluminum alloys, ones withspiral grooves on the inner surface are proposed in order to enhancetheir thermal characteristics. The spiral grooves on the inner surfaceincrease the area of the inner circumference of the tube and alsoimprove wettability by capillary action, thereby winding up therefrigerant and increasing the circumferential length that contributesto heat transfer.

As a conventional method for manufacturing internally spiral groovedtube, a groove rolling method is known in which a grooving plugsupported by a connecting rod is placed inside a tube body, a rollingball is freely rotated circumferentially on the outer side of the tubebody, and the rolling ball presses the outer circumferential wall of thetube body while pulling the tube body out to form the groove (See PatentLiterature 1).

However, when manufacturing inner spiral grooved tubes with smalldiameters by the groove rolling method, it is difficult to shape thespiral grooves. Therefore, a technology has been proposed to formwell-shaped inner spiral grooves by simultaneously applying drawing andtwisting to drawn tubes with straight grooves on the inner surface (seePatent Literature 2).

In addition, by using the method of simultaneously applying the drawingand twisting processes, it has become possible to manufacture internallyspiral grooved tubes with a groove shape in which the groove openingwidth is smaller than the groove bottom width, in other words, withinverted trapezoidal spiral fins in the cross section, which could notbe manufactured using the groove rolling method (see Patent Literature3).

CITATION LIST Patent Literature [Patent Literature 1]

-   Japanese Unexamined Patent Application, First Publication No.    H06-190476

[Patent Literature 2]

-   Japanese Patent (Granted) Publication No. 6391140    [Patent document 3]-   Japanese Unexamined Patent Application, First Publication No.    2018-091610

SUMMARY OF INVENTION Technical Problem

As explained above, various improvements have been made in themanufacturing technology for an aluminum alloy inner spiral groovedtubes. However, in response to recent environmental concerns, there is aneed to further improve the heat transfer characteristics of innerspiral grooved tubes.

The purpose of this invention is to provide inner spiral grooved tubeswith better heat transfer property.

Solution to Problem

The inner spiral grooved tube in accordance with an aspect of thepresent invention is an inner spiral grooved tube including: a tubebody; and a plurality of grooves and a plurality of fins aligned in aninner circumferential direction of the tube body, wherein the groovesand the fins are formed in a spiral along a longitudinal direction ofthe tube body, an outer diameter of the tube body is 3 mm or more and 10mm or less, a number of the fins formed on an inner peripheral surfaceof the tube body is 30 to 60, the inner spiral grooved tube is made of ametal, a cross sectional shape of each of the fins in a cross section ofthe tube body has a rectangular shape having an apex angle of 0±10°, aratio h/f is 0.90 or more and 3.40 or less, h being a fin height and fbeing fin width, a ratio c/f is 0.50 or more and 3.80 or less, c being afin spacing between adjacent fins in the inner circumferential directionof the tube body, and an average obtained by summing the ratio h/f andthe ratio c/f and dividing a sum in half is 0.8 or more and 3.3 or less.

The fins having a rectangular cross sectional shape referred inexplanations of the present invention differ from the high-slim-finshape having an elongated cross sectional shape manufactured by thegroove rolling method, for example for example.

In the inner spiral grooved tube, it is preferable that the fins arearranged with an equal spacing in the inner circumferential direction ofthe tube body.

In the inner spiral grooved tube, it is preferable that the crosssectional shape of each of the fins in the cross section of the tubebody has a rectangular shape having an apex angle of 0±10° and theaverage of the ratio h/f and the ratio c/f is 2.0 or more and 2.8 orless.

In the inner spiral grooved tube, it is preferable that the crosssectional shape of each of the fins has a rectangular shape having anapex angle of 0±5°, and the average of the ratio h/f and the ratio c/fis 2.4 or more and 2.6 or less.

In the inner spiral grooved tube, it is preferable that the tube body ismade of aluminum or an aluminum alloy.

Other aspect of the present invention is a heat exchanger including theinner spiral grooved tube according to any one of the above-describedinner spiral grooved tubes.

Advantageous Effect

According to the aspects of the present invention, it is possible tosecure a long wetted-edge length for the refrigerant flowing inside andto provide an inner spiral-grooved tube with excellent heat transferproperty in which the refrigerant can easily penetrate between the fins,since, in an inner spiral grooved tube having an outer diameter of 3 mmor more and 10 mm or less and 30-60 fins, and made of metal, the crosssectional shape of each of the fins in the cross section of the tubebody has a rectangular shape having an apex angle of 0±10°, the ratioh/f is 0.90 or more and 3.40 or less, h being a fin height and f beingfin width, and the ratio c/f is 0.50 or more and 3.80 or less, c being afin spacing.

If the frontage between the fins is small, it is difficult for therefrigerant to penetrate into the spiral grooves, which tends todeteriorate the heat transfer property. On the other hand, the longerthe wetted-edge length, the better heat transfer property.

In the inner spiral grooved tube having an outer diameter of 3 mm ormore and 10 mm or less and 30-60 fins, and made of metal, therectangular cross sectional fins of the above-described dimension cannotbe manufactured by the conventional rolling method. However, spiralgrooved tubes with spiral fins grooves of the above-described dimensioncan be obtained by a manufacturing method in which twisting and drawingare simultaneously applied to extruded raw tubes.

When the spiral fin height is increased, the fins extend higher towardthe center of the inner spiral grooved tube, so the frontage between thetips of adjacent fins becomes narrower.

In the inner spiral grooved tube having an outer diameter of 3 mm ormore and 10 min or less and 30-60 fins, and made of metal, it isnecessary to secure a minimum frontage for the refrigerant to penetrateinto the tube. In doing so, it is preferable to select theabove-described ranges in relation to the height of the fins, fin topwidth and the number of the on the inner surface of the inner spiralgrooved tube.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front view of an example of a heat exchanger with an innerspiral grooved tube of the first embodiment.

FIG. 2 is a partial view of the example of the heat exchanger.

FIG. 3 is a cross sectional view of the inner spiral grooved tube of thefirst embodiment.

FIG. 4 is a longitudinal sectional view of the inner spiral groovedtube.

FIG. 5 is an explanatory drawing showing an example of the spiral finsgrooves formed on the inner surface of the tube with an inner spiralgroove.

FIG. 6 is an explanatory drawing showing an example of spiral fins andgrooves formed on the inner surface of a conventional tube with an innerspiral groove.

FIG. 7 is a perspective view of an raw tube (straight grooved tube) usedin the manufacturing method of the inner spiral grooved tube.

FIG. 8 is a side view of an example of manufacturing apparatus used inthe production of the inner spiral grooved tubes.

FIG. 9 is a plan view showing a state in which a raw tube is unwound bywinding on the unwinding-side capstan in the manufacturing apparatus ofthe inner spiral grooved tubes.

FIG. 10 is a partially enlarged photograph showing the inner spiralgrooved tube of Example 1.

FIG. 11 is a partially enlarged photograph showing the inner spiralgrooved tube of Example 2.

FIG. 12 is a partially enlarged photograph showing the inner spiralgrooved tube of Example 11.

FIG. 13 is a partially enlarged photograph showing the inner spiralgrooved tube of Example 12.

FIG. 14 is a partially enlarged photograph showing the inner spiralgrooved tube of Comparative Example 1.

FIG. 15 is a partially enlarged photograph showing the inner spiralgrooved tube of Comparative Example 4.

FIG. 16 is a graph showing an example of results measuring thecondensation heat transfer rates of inner spiral grooved tubes ofExamples 1, 11 and 12, and Comparative Example 1.

FIG. 17 is a graph showing an example of results measuring theevaporation heat transfer rates of inner spiral grooved tubes ofExamples 1, 11 and 12, and Comparative Example 1.

FIG. 18 is a graph showing an example of results measuring thecondensation pressure loss of inner spiral grooved tubes of Examples 1,11 and 12, and Comparative Example 1.

FIG. 19 is a graph showing an example of results measuring theevaporation pressure loss of inner spiral grooved tubes of Examples 1,11 and 12, and Comparative Example 1.

DESCRIPTION OF EMBODIMENTS

The following is a description of the embodiment of the invention withreference to the drawings.

In the drawings used in the following explanations, the characteristicparts may be enlarged and highlighted for the sake of convenience. Forthe same purpose, parts that are not characteristic may be omitted fromthe drawings.

FIGS. 1 and 2 show a schematic diagram of a heat exchanger with an innerspiral grooved tube of the first embodiment of the present invention.

In this example, the heat exchanger 1 is constructed with two tubes withinner spiral grooves as tubes through which the refrigerant passes, anda plurality of aluminum plate-like heat dissipating plate 3 are arrangedin parallel around the inner spiral grooved tubes. The innerspiral-grooved tube 2 is a meandering tube. The inner spiral-groovedtube 2 is provided in such a way that it meanders through a plurality ofinsertion holes provided to penetrate the individual heat dissipatingplates 3 arranged in parallel.

In the heat exchanger 1, the inner spiral grooved tube 2 consists ofmain tubes 2A in a U-shaped and elbow tubes 2B in a U-shape. Each of themain tube 2As passes through the heat dissipating plates 3 in a straightline. Each of the elbow tube 2B connects end adjacent openings ofadjacent main tubes 2A. The main tubes 2A in a U-shape and the elbowtubes 2B in a U-shape are formed by bending the inner spiral groovedtube 2 into a U-shape, which will be explained later. An inlet 4 of therefrigerant is formed at one end of the inner spiral-grooved tube 2,which meanders through the heat dissipating plates 3, and an outlet 5 ofthe refrigerant is formed at the other end of the inner spiral-groovedtube 2, thereby forming a heat exchanger 1.

The heat exchanger 1 in this configuration is assembled by mechanicallyjoining the main tubes 2A and the heat dissipating plates 3 by passingthe inner spiral grooved tubes with a slightly smaller diameter than themain tube 2A through the insertion hole in the heat dissipating plates3, expanding the inner spiral grooved tube to form the main tube 2A. Inthe heat exchange 1, connecting the main tubes 3A and the heatdissipating plates 3 is not limited to the above-described mechanicaljoining method. Connecting may be done by other joining method such asbrazing. In terms of tube expansion, any known tube expansion methodssuch as hydraulic, plug, or air expansion may be used.

[Inner Spiral Grooved Tube]

The inner spiral grooved tube 2 used for the heat exchange 1 isspecifically explained below. FIG. 3 is a cross sectional view of theinner spiral grooved tube of the first embodiment.

FIG. 3 is a cross sectional view of the inner spiral grooved tube 2 ofthe first embodiment.

FIG. 4 is a longitudinal sectional view of the inner spiral grooved tube2.

The inner spiral grooved tube 2 in the present embodiment is a twistedmaterial of the extruded raw tube described below. The innerspiral-grooved tube 2 can be made of aluminum or an aluminum alloy. Whenan aluminum alloy is used for the inner spiral grooved tube 2, there areno restrictions on the aluminum alloy to be used. Pure aluminum alloysdefined by JIS, such as 1050 series, 1100 series, 1200 series and thelike can be used. Alternatively, aluminum alloys of 3000 seriesrepresented by 3003 series, to which Mn is added, and the like can beused. In addition, the inner spiral grooved tubes 2 may be constitutedby using any one of other aluminum alloys of 5000 to 7000 series definedby JIS.

In addition, the inner spiral grooved tube 3 may be made of an aluminumalloy not defined by JIS. In this embodiment, the inner spiral-groovedtube 2 made of aluminum or an aluminum alloy is used as an example, butthe heat transfer tube intended in this invention is applicable to anymaterial that can be drawn by a drawing die. Therefore, tubes made ofother alloys, such as copper alloys or iron alloys, may also be used inthe present embodiment.

The inner spiral grooved tube 2 shown in FIG. 3 includes a tube body 6that is circular in cross-sectional outline. The outer diameter of thetube body 6 (the diameter of the circle drawn by the outercircumferential surface 6 a of the tube body 6) is, for example, between3 mm and 10 mm or less. On the inner circumferential surface 6 b of thetube body 6, there are 30 to 60 fins 7 spirally formed along thelongitudinal direction of the tube body 6 at predetermined intervals inthe inner circumferential direction of the tube body 6.

As shown in FIG. 4 , in the inner spiral grooved tube 2, the spiral fin7 and the spiral groove 8 extend with a constant twist angle θ1 in thelongitudinal direction of the tube body 6.

The twist angle θ1 of the individual fin 7 or the spiral groove 8 is theangle between: the extended line of the part drawn in a straight line ofthe spiral groove or the spiral fine shown in the inner central part ofthe tube; and the central axis line of the tube body 2 (or parallellines of the central axis line) in the longitudinal section of the innerspiral grooved tube 2 as shown in FIG. 4 .

By forming spiral fins 7 at predetermined intervals on the inner surface6 b of the tube body 6, the heat exchange efficiency between the innerspiral grooved tube 2 and the refrigerant flowing therein can beincreased. The inner spiral grooved tube 2 with spiral fins 7 can beformed by twisting while drawing the raw tube 9 shown in FIG. 7 , inwhich straight fins and straight grooves extending in a straight line inthe longitudinal direction are formed by the extrusion process. The tube2 can be formed by twisting the raw tube 9 shown in FIG. 7 while drawingit out. FIG. 7 shows an example of fins 9A and grooves 9B formed on theraw tube 9.

As shown in FIG. 3 in a cross-sectional view of a portion of the tubebody 6, the fin 7 is formed in a rectangular shape in the cross section.The rectangular shape is made of the tip part 7 a located on theinterior side of the tube body 6, the bottom part 7 b located on theperiphery side, and a pair of the sidewall parts 7 c located between thetip part 7 a and bottom part 7 b.

The bottom part 7 b of fin 7 is located on the inner circumference ofthe tube body 6 and is continuous with the inner surface 6 h. In otherwords, it is continuous with the bottom surface of the spiral groove 8.The sidewall part 7 c extends linearly along the radial direction of thetube body 6 in the cross-section of the tube body 6 shown in FIG. 3 .The wall thickness from the bottom of the spiral groove 8 to the outercircumference of the tube body 6 in the cross section of the tube body 6can be denoted as the bottom wall thickness (d).

In the inner spiral grooved tube 2 with the structure shown in FIGS. 3and 4 , the plurality of fins 7 are provided in the circumferentialdirection on the inner circumferential surface of the tube body 6. Ineach of the fins 7, the width of the tip part 7 a and the width of thebottom part 7 b are the same or substantially the same. Thus, the widthsof the spiral grooves 8 formed between adjacent fins 7, 7 in thecircumferential direction of the tube body 6 are the same orsubstantially the same on the groove bottom side and the groove openingside

When two fins 7 adjacent to each other in the inner circumferentialdirection of the tube body 6 are shown adjacent to each other on theleft and right as shown in FIG. 5 , the fin height (h) is defined as thedistance from the groove bottom of the spiral groove 8 to the tip part 7a of the fin 7. The fin top width (a) is defined as the width of the tippart 7 a of the fin 7. The fin bottom width (b) is defined as the widthof the bottom part 7 b of the fin 7. The fin spacing (c) is defined asthe spacing between two adjacent fins 7.

In the fin 7 shown in FIG. 5 , since the left and right sidewalls 7 care parallel or substantially parallel, the fin top width (a) and thefin bottom width (b) are the same or substantially the same. Thedefinition of the left and right sidewalls 7 c and 7 c being parallel orsubstantially parallel will be explained later.

In the state shown in FIG. 5 , the fins 7, 7 are depicted in a modelrepresentation and adjacent to each other on the left and right, but asshown in FIG. 3 , the inner surface of the tube body 6 6 b is arc-shapedwith a predetermined curvature. Therefore, the groove width of thespiral groove 8 formed between the adjacent fins 7, 7 is slightly widerat the groove bottom side and gradually narrows toward the grooveopening side.

In the inner spiral grooved tube 2 of this embodiment, the outerdiameter of the tube body 6 is between 3 mm and 10 mm or less, and about30 to 60 fins 7 are formed in the inner circumferential direction of thetube body 6 (30 to 60 strips), for example. The height of fin 7 (theradial dimension of the tube body 6) is between about 0.13 mm or moreand 0.55 mm or less. The bottom wall thickness of the inner spiralgrooved tube 2 (the wall thickness of the tube body 6 corresponding tothe bottom of the spiral groove 8) is between 0.3 mm or more and 0.6 mmor less. The fin top width, which is the thickness of fin 7, is between0.07 mm or more and 0.2 mm or less. The fin top width, which is thethickness of fin 7, is about 0.07 mm or more to 0.2 mm or less.

On the other hand, unlike the fin 7 shown in FIG. 5 , in the case of afin 14, which has a general and conventional structure of isopodtrapezoidal shape as shown in FIG. 6 , the tip part 14 a is formed in aconvex with curvature (a radius) and the sidewalls 14 c, 14 c areslanted so that the tip side is tapered. Therefore, in the fin 14, thecenter of the convex forming the tip of the tip part 14 a is consideredto be the tip of the fin 14. The fin height (h) is defined as thedistance from this center to the bottom of the spiral groove 8. The fintop width (a) is defined as the inside diameter of the convex formingthe tip of the tip part 14 a.

In fin 14, the bottommost portions of sidewalls 14 c, 14 c are close toeach other, and the distance between the bottommost portions of thesidewall parts 14 c, 14 c is defined as the fin spacing (c). Strictlyspeaking, as shown in FIG. 6 , at the bottom of the sidewall parts 14 c,14 c, as shown in FIG. 6 , a radius (concave with curvature) of about0.05 mm is formed in the portion connecting to the bottom surface of thespiral groove 16 in the bottom most portions of the sidewall parts 14 c,14 c. Thus, in such a case, the fin spacing (c) is defined as thedistance between the bottommost portions of sidewall parts 14 c, 14 c onthe left and the right, assuming the locations where the extendedsurfaces of the sidewall part 14 c and the bottom surface of the spiralgroove 16 intersect.

In fin 14 shown in FIG. 6 , the fin widths are different on the upperand lower sides. So in fin 14, the fin width (f) is defined as theaverage of the upper width and the lower width as f=(a+b)/2.

In the fin 14 shown in FIG. 6 , the angle formed by the sidewalls 14 c,14 c is defined as the fin apex angle (θ).

In the fin 7 shown in FIG. 5 , the fin apex angle (θ) is not shown inthe figure because the sidewalls 7 c, 7 c are parallel or practicallyparallel. Thus, In the fin 7, the fin apex angle is defined as 0 whenthe sidewalls 7 c, 7 c are parallel. The fin apex angle, defined as theangle formed by the sidewalls 7 c, 7 c in the fin 7, is in the range of0±10°, and preferably in the range of 0±5°.

Situations that the fin apex angle (θ) is 0±10° include a case where thecross section of the fin 7 is in an isosceles trapezoid shape, each ofthe sidewalls 7 c, 7 c being slanted 0 to +5° in such way that they arenarrowed upward slightly with reference to the fin apex angle (0°) whereeach of the sidewalls 7 c, 7 c are perfectly in parallel. They alsoinclude a case where the cross section of the fin 7 in an inverseisosceles trapezoid shape, each of sidewalls 7 c being slantednegatively to −5° in such a way that they spread upward slightly withreference to the fin apex angle of 0°. In other words, the crosssections of the fins 7 shown in FIGS. 3 and 5 being in a rectangularshape includes a case where the fin apex angle (θ) is slanted in anextent of 0° or more and +5° or less; and a case where the fin apexangle (θ) is slanted in an extent of 0° or less and +5° or more.

As explained above, the fin apex angle being less than 0° or less and−5° or more means that the cross-sectional shape of the fin 7 is in aninverse isosceles trapezoid shape. Similarly, the fin apex angle beingless than 0° or more and +5° or less means that the cross-sectionalshape of the fin 7 is in an isosceles trapezoid shape. Strictlyspeaking, these shapes are not a rectangular shape. However, they arereferred as a rectangular shape as long as the fin apex angle is in arange of 0±10° in this specification.

Similarly, situation that the fin apex angle is in a range of 0±5°includes a case where the cross section of the fin 7 is in an isoscelestrapezoid shape, each of the sidewalls 7 c, 7 c being slanted in such away that they are narrowed upward slightly; and a case where it is in aninverse isosceles trapezoid shape, each of them being slanted in such away that they spread slightly. It means that they includes a case whereeach sidewalls 7 c is slanted 0° or more and +2.5° or less; and a casewhere it is slated 0° or less and −2.5° or more

As explained above, in this embodiment, for convenience, the positivefin apex angle means the case where the cross sectional shape of the fin7 is in an isosceles trapezoid shape with the sidewalls 7 c beingslanted in a positive angle and narrowed upward; and the negative finapex angle means the case where the cross sectional shape of the fin 7is in an inverse isosceles trapezoid shape with the sidewalls 7 c beingslanted in a negative angle and spreading upward.

In the present embodiment of inner spiral grooved tube 2, it ispreferable that the outer diameter is between 3 mm and 10 mm; about 30to 60 fins 7 are formed in the inner circumferential direction; the finheight is 0.13 mm or more and 0.55 mm or less; the bottom wall thicknessis 0.3 mm or more and 0.6 mm or less; and the fin top width is 0.07 mmor more and 0.2 mm or less.

In the inner spiral grooved tube 2 having the above-described dimension,if the fin top width is too wide, the radial opening frontage of thespiral groove 8 becomes too narrow, making it difficult for refrigerantto enter the spiral groove 8, which may worsen heat transferperformance. In addition, the pressure loss of the refrigerantincreases. By setting the fin apex angle to 0±10°, the opening frontageof the spiral groove 8 can be made large enough in the fin 7 having theabove-described dimension, and the flow of refrigerant into the spiralgroove 8 can be ensured. Accordingly, the heat transfer to therefrigerant can be improved and the flow of the refrigerant can besmoothed.

In addition, by setting the fin height and fin top width in theabove-described ranges, the fins 7 can be made thin and long, ensuringsufficient wetting edge length between the refrigerant and the fins andsufficient heat transfer area to ensure good heat transfer coefficient.

In the inner spiral grooved tube 2, the ratio (h/f) of fin height (h) tofin width (f) is set to 0.90 or more and 3.40 or less.

By setting the ratio (h/f) to 0.90 or more, the wetting edge length ofthe fin 7 can be secured as much as possible. If it is below the lowerlimit, the wetting edge length is insufficient. If (h/f) exceeds 3.40,the heat exchange performance will be degraded due to poor refrigerantinflow caused by narrowing of the frontage.

In the inner spiral grooved tube 2, the ratio (c/f) of the distance (c)between fins adjacent to each other in the circumferential direction ofthe tube body to the fin width (f) is set to 0.50 or more and 3.80 orless.

By setting the ratio (c/f) to 0.50 or more, the ease of refrigerantpenetration into the spiral grooves can be ensured. If it is below thelower limit, it becomes difficult for the refrigerant to penetrate intothe spiral grooves. If the ratio (c/f) exceeds 3.80, the wetting edgelength becomes insufficient, and if this is accompanied by a reductionin the number of fin strips, the refrigerant winding effect is reduced,which leads to a decrease in heat exchange performance.

It is preferable that the average value of the ratio (h/f) and the ratio(c/f) is set to 0.8 or more and 3.3 or less, since the heat exchangeperformance varies depending on the balance between the fin height, thefin width, and the fin spacing. Therefore, the average value of theratio (h/f) and the ratio (c/f) is set to 0.8 or more and 3.3 or less.It is preferable that the average value is 2.0 or more and 2.8 or less.It is more preferable that it is 2.4 or more and 2.6 or less.

Conventionally, spiral grooves have been formed on copper-alloy andaluminum-alloy spiral grooved tubes by a manufacturing method generallyreferred to as the groove rolling method. In the groove rolling method,the tube is pressed against a grooved plug on the inner surface of thetube with a rolling ball from the outer circumference of the tube, andgrooves are formed in the valley of the grooved plug by plastic flow.Therefore, even if all grooves were ideally manufactured, the frontageon the apex side (center side of the tube) of the fin 14 was larger thanthat on the bottom side. Moreover, in the groove rolling method, it wasdifficult to achieve the ideal fin 14 shape shown in FIG. 6 , and thefin 14 shape was generally manufactured as a significantly distortedshape.

On the other hand, in the spiral grooved tube 2 of this embodiment,since the fin 7 of the above-described dimension is formed, thesuppression of the film thickness of the refrigerant formed around thefin 7; the effect that refrigerant can easily enter and exit the spiralgroove 8 due to the dimension of the frontage between the fins 7 and 7;and the effect that the wetting edge length is lengthened by thepresence of the rectangular fins 7, can be obtained. By having theabove-described benefits, high evaporation and condensing heat transfercoefficients can be obtained.

<Manufacturing Method>

To produce the rectangular-shaped fin 7 in cross section shown in FIGS.3 and 5 from the raw tube 9 shown in FIG. 7 , as an example, themanufacturing apparatus A shown in FIGS. 8 and 9 can be used.

<Extrusion Forming Step>

A billet made of aluminum or an aluminum alloy is extruded to producethe raw tube 9 shown in FIG. 7 . On the inner surface of this raw tube9, straight fins 9A and straight grooves 9B are formed at equalintervals in the inner circumferential direction.

The corner of the fin 9A and the corner of straight groove 9B, which areformed on the raw tube 9 during the extrusion process, have a radius ofcurvature of 0.05-0.025 mm. Due to the accuracy of the radius ofcurvature, it is possible to produce a rectangular cross-sectional shapeinside the tube with multiple fins equivalent to the cross-sectionalshape shown in FIG. 3 or FIG. 5 .

<Twisting and Drawing Step>

Next, the twisting and drawing step is described.

The twist and drawing step is the process of forming the inner spiralgrooved tube 2 with spiral fins 7 and spiral grooves 8 by applying twistto the above-described raw tube 9 while drawing.

<Manufacturing Apparatus for Twisting and Drawing Step>

FIG. 8 shows a side view of the manufacturing apparatus A for producing2 inner spiral grooved tubes by performing two twist-drawing steps on 9raw tubes. First, an overview of the manufacturing apparatus A isdescribed.

The manufacturing apparatus A includes the revolving mechanism 30, thefloating frame 34, the unwinding bobbin (first bobbin) 11, the firstguide capstan 18, the first drawing die 17, the first revolving capstan21, the revolving flyer 23, the second revolving capstan 22, the seconddrawing die 19, the second guide capstan 61, and the winding bobbin(second bobbin) 71. The details of each part are described below.

(Revolving Mechanism)

The revolving mechanism 30 includes the rotating shaft 35, the driveunit 39, the front stand 37A and the rear stand 37B. The rotating shaft35 includes the front shaft 35A and the rear shaft 35B.

The revolving mechanism rotates the rotating shaft 35, the firstrevolving capstan 21, the second revolving capstan 22 and the revolvingflyer 23. The first revolving capstan 21, the second revolving capstan22 and the revolving flyer 23 are fixed on the rotating shaft 35.

The revolving mechanism 30 is retains the rotating shaft 35 and thefloating frame 34 in a stationary state. The floating frame 34 isarranged coaxially with and supported by the rotating shaft 35.

Both the front shaft 35A and the rear shaft 35B have a hollowcylindrical shape inside. Both the front shaft 35A and the rear shaft35B are arranged on the revolving rotation center axis C (pass line ofthe first drawing die) coaxially. The front shaft 35A is rotatablysupported by the front stand 37A via the bearing type bearing 36 andextends toward the back side (rear stand 37B side) from the front stand37A. Similarly, the rear shaft 35B is rotatably supported by the rearstand 37B via the bearing and extends toward the fore side (front stand37A side) from the rear stand 37B. The floating frame 34 bridges thefront shaft 35A and the rear shaft 35B.

The drive unit 39 includes the drive motor 39 c, the linear motion shaft39 f, the belts 39 a, 39 d, and the pulleys 39 b, 39 e. The drive unit39 rotates the front shaft 35A and the rear shaft 35B.

The drive motor 39 c rotates the linear motion shaft 39 f. The linearmotion shaft 39 f extends forward and backward at the lower part of thefront stand 37A and the rear stand 37 B.

On the fore end part 35Ab of the front shaft 35A, the pulley 39 b isattached on the penetrating tip. The pulley 39 b is linked to the linearmotion shaft 39 f via the belt 39 a. Similarly, on the back end portion35Bb of the rear shaft 35B, the pulley 39 e is attached on thepenetrating tip. The pulley 39 e is linked to the linear motion shaft 39f via the belt 39 d. As a result, the front shaft 35A and the rear shaft35B rotate synchronously about the revolving rotation center axis C.

The first revolving capstan 21, the second revolving capstan 22 andrevolving flyer 23 are fixed to the rotating shaft 35 (the front shaft35A and the rear shaft 35B). As the rotary shaft 35 rotates, thesecomponents fixed to the rotary shaft 35 revolve and rotate about therevolving rotation center axis C.

(Floating Frame)

The floating frame 34 is supported by the front shaft 35A and the rearshaft 35B of the rotating shaft 35 on the end portion 35Aa of the frontshaft 35A and the end portion 35Ba of the rear shaft 35B via thebearings 34 a. The end portion 35Aa and the end portions 35Ba face eachother. The floating frame 34 supports the unwinding bobbin 11, the firstguide capstan 18 and the first drawing die 17.

FIG. 9 is a plan view of the floating frame 34 viewed from the directionof arrow X in FIG. 8 . As shown in FIGS. 8 and 9 , the floating frame 34has the box shape with openings at the top and bottom. The floatingframe 34 includes the front wall 34 b and the rear wall 34 c facingfront and rear. In addition, the floating frame 34 includes thesupporting walls 34 d that face on left and right and extend in theforward and backward directions.

The front wall 34 b and the rear wall 34 c are provided with throughholes. Each of the end portion 35Aa of the front shaft 35A and the endportion 35Ba of the rear shaft 35B penetrates through each of thethrough holes. One of bearings 34 a is interposed between each of theend portions 35Aa and 35Ba and each of the through holes of the frontwall 34 b and the rear wall 34 c. This made it harder for the rotationof the rotating shaft 35 (the front shaft 35A and the rear shaft 35B) tobe transmitted to the floating frame 34. The floating frame 34 isretained in stationary with respect to the ground U even if the rotatingshaft 35 is in a rotating state. The stationary state of the floatingframe 34 may be stabilized by installing a weight that biases the centerof gravity of the floating frame 34 with respect to the revolvingrotation center axis C.

As shown in FIG. 9 , the pair of support walls 34 d are arranged on bothsides of the unwinding bobbin 11, the first guide capstan 18 and thefirst drawing die 17 on both sides in the left-right direction (verticaldirection in FIG. 9 paper plane). The pair of support walls 34 d areused to support the bobbin support shaft 12 holding the unwinding bobbin11 and the rotationally supporting the rotation shaft J18 of the firstguide capstan 18. The support walls 34 d also support the first drawingdie 17 via the die support, which is not shown in the figure.

(Unwinding Bobbin)

The unwinding bobbin 11 is wound with the raw tube 9. The unwindingbobbin 11 winds out the raw tube 9 and supplies it to the subsequentstage. The unwinding bobbin 11 is removably attached to the bobbinsupport shaft 12.

As shown in FIG. 8 , the bobbin support shaft 12 extends orthogonally tothe rotating shaft 35. The bobbin support shaft 12 is supported by thefloating frame 34 in a self-rotating manner. The rotation means rotationaround the center axis of the bobbin support shaft 12 itself. The bobbinsupport shaft 12 holds the unwinding bobbin 11 and rotates by itself inthe feeding direction of the unwinding bobbin 11, assisting theunwinding of the raw tube 9 from the bobbin 11.

The bobbin support shaft 12 is provided with the brake part 15. Thebrake part 15 applies braking force to the self-rotation of the bobbinsupport shaft 12 with respect to the floating frame 34. In other words,the brake part 15 regulates the rotation of the unwinding bobbin 11 inthe unwinding direction. The braking force by the brake part 15 addsbackward tension to the raw tube 9 being conveyed in the unwindingdirection.

(First Guide Capstan)

The first guide capstan 18 has a disk shape. The first guide capstan 18is used to wind the raw tube 9 from the unwinding bobbin 11 around thefirst guide capstan 18. The first guide capstan 18 is wound around acircumference of the raw tube 9. The tangential direction of the outercircumference of the first guide capstan 18 coincides with the revolvingrotation center axis C. The first guide capstan 18 guides the raw tube 9along the first direction D1 onto the revolving rotation center axis C.

The first guide capstan 18 is supported by the floating frame 34 in arotationally free manner. The guide rollers 18 b, which rotate freely ontheir own axis, are arranged in a row around the periphery of the firstguide capstan 18 and. The first guide capstan 18 of this embodiment hasguide rollers 18 b that rotate individually and the raw tube 9 isconveyed smoothly. In FIG. 8 , the guide rollers 18 b arc omitted.

As shown in FIG. 8 , between the first guide capstan 18 and theunwinding bobbin 11, the tube route guiding part 18 a is provided. Thetube route guiding part 18 a is, for example, guide rollers arranged tosurround the raw tube 9. The tube route guiding part 18 a guides the rawtube 9 supplied from the unwinding bobbin 11 to the first guide capstan18.

(First Drawing Die)

The first drawing die 17 reduces the diameter of the raw tube 9. Thefirst drawing die 17 is fixed to the floating frame 34. The drawingdirection of the first drawing die 17 is the first direction D1. Thecenter of the first drawing die 17 coincides with the revolving rotationcenter axis C of the rotating shaft 35. The first direction D1 isparallel to the revolving rotation center axis C.

The first drawing die 17 is supplied with a lubricating oil by thelubricating oil supply unit 34 A, which is fixed to the floating frame34.

The intermediate twisted tube 9D, which has passed through the firstdrawing die 17, is introduced into the front wall 34 b of the floatingframe 34 and is introduced into the interior of the front shaft 35Athrough the through hole.

(First Revolving Capstan)

The first revolving capstan 21 has a disk shape. The first revolvingcapstan 21 has the side hole 34Ac that radially penetrates through theinside and outside of the hollow front shaft 35A. The first revolvingcapstan 21 is supported by the support 21 a fixed on the outer peripherypart of the rotating shaft 35 (the front shaft 35A) having the center ofthe disk as the axis of rotation J21.

The first revolving capstan 21 has one of its outer circumferencetangents coincides with the revolving rotation center axis C.

The raw tube 9 that is conveyed in the first direction D1 on therevolving rotation center axis C is wound more than once on the firstrevolving capstan 21. The first revolving capstan 21 winds the tubematerial and draws it outside from the inside of the front shaft 35A andguides it to the revolving flyer 23.

The first revolving capstan 21 revolves with the front shaft 35A aroundthe revolving rotation center axis C. The revolving rotation center axisC extends orthogonally to the rotation axis J21 of the revolution of thefirst revolving capstan 21. The tube material is given a twist betweenthe first revolving rotation capstan 21 and the first drawing die 17. Bythis first drawing and twisting step, the raw tube 9 is processed intothe intermediate twisted tube 9D.

Together with the first revolving capstan 21, the drive motor 20 isprovided to the front shaft 35A. The drive motor 20 drives and rotatesthe first revolving capstan 21 in the winding direction (the conveyingdirection) of the tube material. Thereby, the first revolving capstan 21imparts a forward tension to the tube material to pass through the firstdrawing die 17.

(Revolving Flyer)

The revolving flyer 23 reverses the tube route of the intermediatetwisted tube 9D between the first drawing die 17 and the second drawingdie 19. The revolving flyer 23 reverses the intermediate twisted tube 9Dand directs the conveying direction toward the second direction D2,which is the drawing direction of the second drawing die 19. Morespecifically, the revolving flyer 23 guides the intermediate twistedtube 9D from the first revolving capstan 21 to the second revolvingcapstan 22.

The revolving flyer 23 includes guide rollers 23 a and the guide rollersupports (not shown in the figure) that support the guide rollers 23 a.The guide roller supports are supported by the rotating shaft 35,although the illustration of the guide roller supports is omitted hereto eliminate complexity. However, the guide rollers are not essentialfor the structure of the flyer; it can be a plate-like structure with aring for the tube to pass through.

The guide rollers 23 a are arranged in parallel forming an outwardlycurved arch shape relative to the revolving rotation center axis C. Theguide rollers 23 a themselves roll to convey the intermediate twistedtube 9D smoothly. The revolving rotation flyer 23 revolves around: thefloating frame 34; and the first drawing die 17 and the unwound bobbin11 that are supported inside of the floating frame 34, centering on therevolving rotation center axis C.

One end of the revolving rotation flyer 23 is located outside the firstrevolving rotation capstan 21 relative to the revolving rotation centeraxis C. The other end of the revolving rotation flyer 23 passes throughthe side hole 35Bc that radially penetrates through the inside andoutside of the hollow rear shaft 35B, and extends to the inside of therear shaft 35B. The revolving flyer 23 guides the intermediate twistedtube 9D that is let out by being wounded up on the first revolvingcapstan 21 to the side of the rear shaft 35B. In addition, the revolvingcapstan 23 feed the intermediate twisted tube 9D in such a way that theintermediate twisted tube 9D coincides with the revolving rotationcenter axis C along the second direction D2 inside of the rear shaft35B.

(Second Revolving Capstan)

The second revolving capstan 22 has a disk shape similar to the firstrevolving capstan 21. The second revolving capstan 22 is supported bythe support 22 a in a state of free rotation. The support 22 a isprovided on the tip of the end portion 35Bb of the rear shaft 35B. Inaddition, the guide rollers 22 c that rotate themselves freely arearranged side by side on the outer periphery of the second revolvingcapstan 22. In the second revolving capstan 22 of the presentembodiment, each of the guide rollers 22 c rotate individually. Therotation of them allows smooth conveying of the tube material.

The second revolving capstan 22 has one of its outer circumferencetangents coincides with the rotation center axis C.

On the second revolving capstan 22, the tube material 5 conveyed in thesecond direction D2 on the rotation center axis C is wound around thesecond revolving capstan 22. The second revolving capstan 22 feeds thewound tube material in the second direction D2 on the rotation centeraxis C.

The second revolving capstan 22 rotates with the rear shaft 35B aroundthe rotation center axis C. The rotation center axis C is extended inthe direction orthogonal to the rotation axis J22 of the secondrevolving capstan 22. The intermediate twisted tube 9D, which is fedfrom the second revolving capstan 22, is reduced in diameter in thesecond drawing die 19. Since the second drawing die 19 is stationarywith respect to the ground G, twist is applied to the intermediatetwisted tube 9D between the second revolving capstan 22 and the seconddrawing die 19. With this second drawing and twisting step, theintermediate twisted tube 9D is processed into an inner spiral groovedtube 2.

The support 22 a, which supports the second revolving capstan 22,supports the weight 22 b on the location symmetrical to the secondrevolving capstan 22 with respect to the rotation center axis C. Theweight 22 b stabilizes the balance of the rotation of the rear shaft35B.

(Second Drawing Die)

The second drawing die 19 is located at the rear of the second revolvingcapstan 22. The second drawing die 19 has the opposite second directionD2 as the drawing direction. The second direction D2 is parallel to therotation center axis C. The second direction D2 is opposite to the firstdirection D1, which is the drawing direction of the first drawing die17. The intermediate twisted tube 9D passes through the second drawingdie 19 along the second direction D2. The second drawing die 19 isstationary with respect to the ground G. The center of the seconddrawing die 19 coincides with the rotation center axis C of the rotatingshaft 35.

The second drawing die 19 is supported on the frame 62, for example, viaa die support not shown in the figure. The second drawing die 19 issupplied with a lubricating oil by the lubricating oil supply unit 62A,which is mounted on the frame 62. This reduces the pulling force on thesecond drawing die 19.

(Second Guide Capstan)

The second guide capstan 61 has a disk shape. The tangential directionof the outer circumference of the second guide capstan 61 coincides withthe revolving rotation center axis C. The inner spiral grooved tube 2that is conveyed in the second direction D2 on the revolving rotationcenter axis C is wounded up on the second guide capstan 61 more thanonce.

The second guide capstan 61 is supported by the frame 62 in a rotationfree manner around the rotation axis J61. The rotation axis J61 of thesecond guide capstan is linked with the drive motor 63 via a drive beltor the like. The second guide capstan 61 is driven and rotated by thedrive motor 63 in the winding direction (the conveying direction) of theinner spiral grooved tube 2. It is preferable that the drive motor 63 isa torque motor that can control torque.

The second guide capstan 61 is driven to apply forward tension to theinner spiral grooved tube 2. As a result, the inner spiral grooved tube2 is fed forward with the necessary drawing stress for processing on thesecond drawing die 19.

(Winding Bobbin)

Winding bobbin 71 is provided at the end of the tube route of the innerspiral grooved tube 2 to recover the inner spiral grooved tube 2. Thepulley 72 is provided at the front of the winding bobbin 71.

The winding bobbin 71 is removably attached to the bobbin support shaft73. The bobbin support shaft 73 is supported on the frame 75 andconnected to the drive motor 74 via a drive belt or the like.

<Twisting and Drawing Step>

The method of manufacturing the inner spiral grooved tube 2 using themanufacturing apparatus A described above will be described below.

The raw tube 9 is set in the tube route in advance by feeding the rawtube 9 from the unwound bobbin 11. The setting is done by allowing theraw tube 9 to pass through: the first guide capstan 18; the firstdrawing die 17; the first revolving capstan 21; the revolving flyer 23;the second revolving capstan 61; the second drawing die 19; the secondguide capstan; and the winding bobbin 71, in the order.

The first guide capstan 18 guides the raw tube 9 into the die hole ofthe first drawing die 17 located on the rotation center axis C.

Next, the raw tube 9 is passed through the first drawing die 17.Furthermore, the tube material is wound around the first revolvingcapstan 21 at the rear of the first drawing die 17 and rotated aroundthe rotation axis. This reduces the diameter of the raw tube 9 and givesit a twist (first twisting and drawing step).

In the first twisting and drawing step, it is possible to apply anappropriate tension to the raw tube 9, which provides a stable twistangle without causing the tube material 5 to buckle or rupture.

By drawing the raw tube 9 through the first drawing die 17 and by thefirst revolving capstan, a twist is applied to the raw tube 9. Becauseof this, a twist is imparted to the straight fins 9A and the straightgrooves 9B inside the raw tube 9.

The first twisting and drawing step makes the raw tube 9 into theintermediate twisted tube 9D. The intermediate twisted tube 9D is a tubematerial at an intermediate stage in the manufacturing process of theinner spiral grooved tube 2. It is in a state where fins and grooveshaving a shallower twist angle than the fins 7 and the grooves 9 of theinner spiral grooved tube 2 are formed.

Next, the intermediate twisted tube 9D is wound around the revolvingflyer 23, and the conveyance direction is directed in the seconddirection D2 on the rotation center axis C. Further, the intermediatetwisted tube 9D is wound around the second revolving capstan 22, and theintermediate twisted tube 9D is introduced into the second drawing die19.

Next, the intermediate twisted tube 9D, which rotates with the secondrevolving capstan 22, is passed through the second drawing die 19. Thisreduces the diameter of the intermediate twisted tube 9D and applies atwist to the intermediate twisted tube 9D, further increasing the leadangle (the second twisting and drawing step). Through this secondtwisting and drawing step, the intermediate twisted tube 9D becomes theinner spiral grooved tube 2. Here, the inner spiral grooved tube 2 withthe desired lead angle can be obtained.

<Finishing Drawing Step>

Next, the inner spiral grooved tube 2 is passed through the finishingdrawing die 70 (the finishing drawing step). The surface of the innerspiral grooved tube 2 is ideally shaped by passing through the finishingdrawing die 70.

According to the twisting and drawing step using manufacturing apparatusA described above, since twisting and drawing are performedsimultaneously, it is possible to reduce the shear stress required fortwisting in order to apply a combined stress of twisting and diameterreduction to the raw tube 9. Accordingly, a large amount of twist can beapplied to the raw tube 9 before the buckling stress of the raw tube 9is reached to the limit.

By reducing the wall thickness, the inner spiral grooved tube 2 can bemade lighter and less expensive by reducing the material cost. In otherwords, according to this embodiment, lightweight, inexpensive, andhighly efficient heat exchange inner spiral grooved tube 2 can bemanufactured.

According to manufacturing apparatus A shown in FIGS. 8 and 9 , thetwisting directions in the first twisting and drawing step and thesecond twisting and drawing step are matched to give twist to the rawtube 9, facilitating mass production.

When only twist is applied to a thin tube 9, such as 3 to 10 mm, made ofaluminum or an aluminum alloy, it easily buckles or breaks. In thismanufacturing apparatus A, the drawing is applied simultaneously withthe twisting to suppress buckling and rupture caused by twisting whiledrawing, so that even the above-mentioned size of raw tube 9 can betwisted without buckling or rupture.

In this specification, manufacturing apparatus A shown in FIGS. 8 and 9is used as the manufacturing apparatus for manufacturing the innerspiral grooved tube 2 from the raw tube 9, but the manufacturingapparatus is not limited to this example. However, the manufacturingapparatus is not limited to this example, and other manufacturingapparatus that performs the twisting and drawing step described inPatent Publication No. 2016-22505, etc. may also be applied.

Varieties of extruded raw tubes having different sizes were produced byextruding raw tubes made of JISA3003 aluminum alloy from a billet. Eachof them had a number of straight fins and a number of straight groovesalternately and equally spaced along the inner circumference and theentire length.

Next, those tubes were subjected to the twisting and drawing step usingthe manufacturing apparatus A shown in FIGS. 8 and 9 to produce theinner spiral grooved tubes of Examples 1-13 of the present invention andComparative Examples 1-11. Table 1 shows the results of measuring thebottom wall thickness (mm), the fin height (mm), and the fin top width(mm) of the inner spiral grooved tubes in Examples 1, 2, 11, and 12 orthe present invention; and Comparative Examples 1, 4. In addition, theaverage values of these values at eight circumferential locations areshown in Table 1.

TABLE 1 1 2 3 4 5 6 7 8 AVE Example 1 Whole 0.819 0.806 0.807 0.7870.792 0.790 0.812 0.803 0.802 Bottom thickness 0.460 0.439 0.449 0.4380.446 0.445 0.441 0.442 0.445 Fin height 0.359 0.367 0.358 0.349 0.3460.345 0.371 0.361 0.357 Fin top width 0.125 0.129 0.123 0.110 0.1320.135 0.128 0.124 0.126 Example 2 Whole 0.636 0.663 0.683 0.689 0.6690.652 0.627 0.625 0.656 Bottom thickness 0.419 0.433 0.448 0.452 0.4420.421 0.409 0.408 0.429 Fin height 0.217 0.230 0.235 0.237 0.227 0.2310.218 0.217 0.227 Fin top width 0.094 0.091 0.102 0.098 0.091 0.0970.093 0.092 0.095 Example 11 Whole 0.714 0.718 0.722 0.732 0.724 0.7280.728 0.714 0.723 Bottom thickness 0.437 0.442 0.447 0.442 0.439 0.4330.435 0.429 0.438 Fin height 0.277 0.276 0.275 0.29 0.285 0.295 0.2930.285 0.285 Fin top width 0.116 0.106 0.091 0.117 0.118 0.121 0.1090.112 0.111 Example 12 Whole 0.719 0.727 0.729 0.739 0.763 0.758 0.7670.741 0.743 Bottom thickness 0.432 0.434 0.436 0.444 0.457 0.462 0.4700.463 0.450 Fin height 0.287 0.293 0.293 0.295 0.306 0.296 0.297 0.2780.293 Fin top width 0.170 0.167 0.185 0.161 0.176 0.171 0.171 0.1610.170 C. Example 1 Whole 0.694 0.682 0.687 0.697 0.690 0.698 0.698 0.6960.693 Bottom thickness 0.425 0.422 0.418 0.420 0.417 0.432 0.432 0.4310.425 Fin height 0.269 0.260 0.269 0.277 0.273 0.266 0.266 0.265 0.268Fin top width 0.115 0.108 0.111 0.118 0.103 0.109 0.100 0.102 0.108 Apexangle 26.1 28.5 22.6 22.4 25.0 22.8 22.4 25.4 24.40 C. Example 4 Whole0.569 0.574 0.578 0.568 0.578 0.577 0.572 0.566 0.573 Bottom thickness0.400 0.400 0.393 0.390 0.406 0.401 0.396 0.397 0.398 Fin height 0.1690.174 0.185 0.178 0.172 0.176 0.176 0.169 0.175 Fin top width 0.1580.166 0.164 0.167 0.153 0.152 0.154 0.166 0.160 Apex angle 31.1 29.629.8 27.5 29.8 29.7 30.8 30.8 29.90 (unit: mm)

In addition, Tables 2 and 3 below show the results for Examples 1, 2,11, and 12 of the present invention and Comparative Examples 1 and 4.The bottom wall thickness; the fin height (h: mm), the fin top width (a:mm), the spacing between fins (c mm), the fin width (f mm), the value ofh/f, and the value of c/f, all of which were obtained from the averagevalues in Table 1, are shown in Tables 2 and 3. In addition, the outerdiameter of each inner spiral grooved tube; the number of strips; thefin apex angle)(°); the flow channel area (mm²); the wetted edge length(mm); and the heat exchange performance of a single tube; the averagevalue of the ratio h/f and the ration c/f are shown in Tables 2 and 3.Table 2 also shows results of other Examples and Comparative examples,measured in the same way as in Table 1 and obtained results as inExamples 1, 2, 11, and 12 and Comparative Examples 1 and 4.

The heat exchange performance of a single tube was evaluated using adouble-tube structure. Refrigerant flowed in the inner tube (heattransfer tube) and water flowed in the outer tube in countercurrent, andthe heat transfer coefficient in the inner tube was calculated from thetemperature change at the inlet/outlet of the water. The pressure losswas evaluated by calculating the refrigerant pressure difference at theinlet/outlet of the inner tube.

The heat exchanger performance was evaluated in the heat exchangerperformance evaluation results with a single tube at a refrigerant flowrate of approximately 20 kg/h. When the heat transfer coefficient ofcondensation was 6.5 kW/m²×° C. or less and the heat transfercoefficient of evaporation was 8.0 kW/m²×° C. or less, it was ranked asD (Bad).

When the heat transfer coefficient of condensation is more than 6.5kW/m²×° C. and 8.0 kW/m²×° C. or less, and the heat transfer coefficientof evaporation was more than 8.0 kW/m²×° C. and 12.0 kW/m²×° C. or less,it was ranked as C (Mediocre).

When the heat transfer coefficient of condensation is more than 8.0kW/m²×° C. and 9.5 kW/m²×° C. or less, and the heat transfer coefficientof evaporation was more than 8.0 kW/m²×° C. and 12.0 kW/m²×° C. or less,it was ranked as B (Good).

When the heat transfer coefficient of condensation is more than 9.5kW/m²×° C., and the heat transfer coefficient of evaporation was morethan 12.0 kW/m²×° C., it was ranked as A (Very Good).

TABLE 2 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Example 7 Example 8 Outer diameter mm 7.02 7.02 7.02 7.02 7.02 7.02 7.027.02 Bottom thickness d (mm) 0.445 0.429 0.493 0.495 0.489 0.493 0.4940.497 Fin height h (mm) 0.357 0.227 0.140 0.348 0.196 0.230 0.392 0.241Fin top width a (mm) 0.126 0.095 0.159 0.118 0.104 0.193 0.124 0.143Strip number Strips 40 45 35 60 35 60 60 35 Fin apex angle θ (°) 0 0 −5−5 5 5 0 −2.5 Fin spacing c (mm) 0.269 0.254 0.395 0.228 0.421 0.1030.192 0.408 Fin width f = (a + b)/2 0.123 0.091 0.153 0.103 0.113 0.2030.124 0.138 h/f 2.902 2.495 0.916 3.385 1.741 1.133 3.161 1.750 c/f2.187 2.791 2.583 2.220 3.742 0.507 1.547 2.965 Flow channel area mm²27.7 28.9 27.8 26.4 27.9 25.8 25.7 27.4 Wetted edge length mm 44.4 36.129.2 62.6 32.1 45.4 66.0 36.2 Single tube heat A A C B B C A A transferperformance Average of the ratio 2.5 2.6 1.7 2.8 2.7 0.8 2.4 2.4 h/f andthe ratio c/f C. Example C. Example C. Example Example 9 Example 10Example 11 Example 12 Example 13 1 2 3 Outer diameter mm 7.02 7.02 7.027.02 7.02 7.02 7.02 7.02 Bottom thickness d (mm) 0.488 0.501 0.438 0.4500.450 0.425 0.445 0.445 Fin height h (mm) 0.285 0.432 0.285 0.293 0.2930.268 0.442 0.355 Fin top width a (mm) 0.131 0.119 0.111 0.170 0.1700.108 0.126 0.125 Strip number Strips 35 30 45 45 30 45 30 25 Fin apexangle θ (°) 2.5 5 0 0 0 24.4 0 0 Fin spacing c (mm) 0.399 0.474 0.2330.179 0.350 0.149 0.270 0.504 Fin width f = (a + b)/2 0.137 0.138 0.1120.163 0.163 0.152 0.122 0.123 h/f 2.077 3.134 2.540 1.798 1.798 1.7643.623 2.887 c/f 2.908 3.435 2.080 1.098 2.147 0.980 2.213 4.098 Flowchannel area mm² 27.3 26.7 28.2 27.2 27.9 27.9 27.8 28.4 Wetted edgelength mm 38.5 43.7 41.1 42.1 33.2 36.3 38.4 33.5 Single tube heat A C BC B D D D transfer performance Average of the ratio 2.5 3.3 2.3 1.4 2.01.4 2.9 3.5 h/f and the ratio c/f

TABLE 3 C. Example C. Example C. Example C. Example C. Example C.Example C. Example C. Example 4 5 6 7 8 9 10 11 Outer diameter mm 7.027.02 7.02 7.02 7.02 7.02 7.02 7.02 Bottom thickness d (mm) 0.398 0.4980.503 0.502 0.495 0.496 0.499 0.497 Fin height h (mm) 0.175 0.255 0.4080.080 0.461 0.110 0.436 0.252 Fin top width a (mm) 0.160 0.296 0.1270.138 0.121 0.220 0.101 0.112 Strip number Strips 40 50 35 35 50 60 6535 Fin apex angle θ (°) 29.9 −10.0 −5 5 −2.5 2.5 5 0 Fin spacing c (mm)0.236 0.127 0.448 0.395 0.278 0.091 0.152 0.429 Fin width f = (a + b)/20.206 0.274 0.109 0.141 0.111 0.222 0.120 0.112 h/f 0.848 0.932 3.7370.565 4.156 0.495 3.633 2.250 c/f 1.145 0.466 4.108 2.792 2.506 0.4081.267 3.829 Flow channel area mm² 29.0 25.0 26.8 28.0 26.0 27.1 25.127.5 Wetted edge length mm 30.3 46.8 48.7 24.3 66.1 31.9 73.2 36.6Single tube heat D D D D D D D D transfer performance Average of theratio 1.0 0.7 3.9 1.7 3.3 0.5 2.4 3.0 h/f and the ratio c/f

FIG. 10 shows a part of the cross section of the inner spiral groovedtube according to Example 1 of the present invention.

FIG. 11 shows a part of the cross section of the inner spiral groovedtube according to Example 2 of the present invention.

FIG. 12 shows a part of the cross section of the inner spiral groovedtube according to Example 11 of the present invention.

FIG. 13 shows a part of the cross section of the inner spiral groovedtube according to Example 12 of the present invention.

FIG. 14 shows a part of the cross section of the inner spiral groovedtube according to Comparative Example 1.

FIG. 15 shows a part of the cross section of the inner spiral groovedtube according to Comparative Example 4.

In the case of the inner spiral grooved tubes of Examples 1 to 13 of thepresent invention as shown in FIGS. 10 to 13 , the fin apex angle is setto 0±10° and the cross section is rectangular, so that fins with goodheat transfer efficiency can be provided.

In the inner spiral grooved tubes of Examples 1 to 13 of the presentinvention, the ratio (h/f) of the fin height (h) to the fin width (f)was 0.90 or more and 3.40 or less, so that the wet edge length of therefrigerant can be increased. In addition, the inner spiral grooved tubehaving good heat transfer efficiency can be provided.

In the inner spiral grooved pipes of Examples 1 to 13, the ratio (c/f)of the distance (c) between the fins adjacent to each other in thecircumferential direction of the tube body and the fin width (f) was setin the range of 0.50 or more and 3.80 or less. Therefore, the distancebetween the fins could be widened, and the frontage was secured so thatthe refrigerant could easily enter the spiral groove. As a result, itwas possible to

In the inner spiral grooved pipes of Examples 1, 2, 7, 8 and 9 of thepresent invention, the fin apex angle was 0±5°. In addition, the averagevalue of the ratio (h/f) of the fin height (h) to the fin width (f) andthe ratio (c/f) of the fin spacing between fins adjacent to each otherin the circumferential direction of the tube body and the fin width (f)was set in the range of 2.4 to 2.6. As a result, it was possible toprovide an inner spiral grooved tube having better heat transferefficiency.

On the other hand, the inner spiral grooved tube of Example 11 had thefin apex angle of 0±5°. Further, the average value of the ratio (h/f)and the ratio (c/f) was within the desired range. Therefore, even if thewet edge length was the same as that of Examples 1 and 2, the heatexchange performance was slightly deteriorated in Example 11.

Next, the inner spiral grooved tube of Example 12 had the fin apex angleof 0±5°. Further, the ratio (h/f) was 1.8, and the ratio (c/f) was 1.1,both of which were values in the desired range. However, since theaverage value of the ratio (h/f) and the ratio (c/f) was less than 1.8,the heat exchange performance was lower than Examples 1 and 2, andslightly lower than that of Example 11.

Next, in the inner spiral grooved tube of Comparative Example 1, theaverage value of the ratio (h/f) and the ratio (c/f) was within thedesired range. However, since the fin apex angle was wide, the thinliquid film could not be formed by a large amount of inflowingrefrigerant. Thus, the heat exchange performance deteriorated becausethe drying phenomenon did not occur efficiently.

Next, in the inner spiral grooved tube of Comparative Example 2, theaverage value of the ratio (h/f) and the ratio (c/f) was out of thedesired range to the upper side, which meant that there were relativelythin and high fins formed circumferentially. However, the spacingbetween the fin troughs became wider, resulting in a similar tendency ofdeteriorated heat exchange performance.

In Comparative Example 3, the number of fins was small, and the ratio(c/f) was 4.1, which was out of the desired range on the upper side. InComparative Example 3, the thermal characteristics were deteriorated inthe same tendency.

Next, the inner spiral grooved tube of Comparative Example 4 had a largefin apex angle and the ratio (h/f) of 0.85, which was out of the desiredrange downward. In addition, the presence of short fins in thecircumferential direction reduced the length of the wet edge anddeteriorated the heat exchange performance. In Comparative Examples 6 to9, either or both of the ratio (h/f) and the ratio (c/f) deviated fromthe desired range to the lower side or the upper side, and the heatexchange performance deteriorated in the same tendency.

Next, the inner spiral grooved tube of Comparative Example 5 had a largefin apex angle on the negative side and the ratio (c/f) of 0.47, whichwas out of the desired range on the downward side. As a result, thefrontage of the fin top was narrowed, so that the refrigerant did notflow efficiently and the heat exchange performance deteriorated. InComparative Example 10, the number of fins was large and the ratio (h/f)was 3.6, which was out of the desired range on the upper side. InComparative Example 10, the heat exchange performance deteriorated inthe same tendency.

Next, in the inner spiral grooved tube of Comparative Example 11, theratio (c/f) was out of the desired range upward, and the wet edge lengthwas long. In Comparative Example 11, it became difficult to form a thinrefrigerant film due to the wide space between the fins, and the heatexchange performance deteriorated due to inefficient drying.

The following shows some results when the heat exchange performance ofthe inner spiral grooved tube was evaluated by the evaluation methodshown above.

The graph shown in FIG. 16 shows the results of measuring the heattransfer coefficient of condensation for the inner spiral grooved tubesof Example 1 (A), Example 11 (B), Example 12 (C), and ComparativeExample 1 (D). The graph shown in FIG. 17 shows the results of measuringthe heat transfer coefficient of evaporation for the inner spiralgrooved tubes of Example 1 (A), Example 11 (B), Example 12 (C), andComparative Example 1 (C).

As shown in the graphs shown in FIGS. 16 and 17 , it is clear that theheat transfer coefficient was improved in the inner spiral grooved tubesof Examples 1, 11 and 12 from the results of both condensation heattransfer and evaporation heat transfer with respect to the inner spiralgrooved tube of Comparative Example 1.

Based on the above-described results, it can be concluded that it ispossible to secure a long wet edge length of the refrigerant flowinginside, and to provide an inner spiral grooved tube having excellentheat transfer property in which the refrigerant easily enters betweenthe fins, by configuring the spiral fins to have a rectangular crosssectional shape with the fin apex angle in the range of 0±10°, 0.90 ormore and 3.40 or less of the ratio h/f between the height and the width,and 0.50 or more and 3.80 or less of the ratio c/f between the spacingand the width, in an inner spiral grooved tube made of a metal having anouter diameter of 3 mm or more and 10 mm or less and having 30 to 60fins.

As shown in the graphs shown in FIGS. 16 and 17 , these relationshipsremained unchanged as the refrigerant flow rate increased or decreased.Therefore, it is clear that the inner spiral grooved tube of Example 1had an improved heat transfer coefficient in both condensation andevaporation heat transfer compared to the inner spiral grooved tube ofComparative Example 1.

Depending on the shape of the inner grooves, the heat transferperformance varied. In the heat exchanger performance evaluation at arefrigerant flow rate of approximately 20 kg/h, when the heat transfercoefficient of condensation was 6.5 kW/m²×° C. or less and the heattransfer coefficient of evaporation was 8.0 kW/m²×° C. or less, it wasranked as D (Bad). When the heat transfer coefficient of condensation ismore than 6.5 kW/m²×° C. and 8.0 kW/m²×° C. or less, and the heattransfer coefficient of evaporation was more than 8.0 kW/m²×° C. and12.0 kW/m²×° C. or less, it was ranked as C (Mediocre). When the heattransfer coefficient of condensation is more than 8.0 kW/m²×° C. and 9.5kW/m²×° C. or less, and the heat transfer coefficient of evaporation wasmore than 8.0 kW/m²×° C. and 12.0 kW/m²×° C. or less, it was ranked as B(Good). When the heat transfer coefficient of condensation is more than9.5 kW/m²×° C., and the heat transfer coefficient of evaporation wasmore than 12.0 kW/m²×° C., it was ranked as A (Very Good).

The graph shown in FIG. 18 shows the results of measuring thecondensation pressure loss of the inner spiral grooved tube of Example 1(A), Example 11 (13), Example 12 (C), and Comparative Example 1 (C). Thegraph shown in FIG. 19 shows the results of measuring the evaporationpressure loss of the inner spiral grooved tube of Example 1 (A), Example11 (B), Example 12 (C), and Comparative Example 1 (C).

From the comparison between the graph shown in FIG. 18 and the graphshown in FIG. 19 , the followings can deduced by comparing the innerspiral grooved tube of Examples 1, 11 and 12 with the inner spiralgrooved tube of Comparative Example 1. In these cases, the values of thecondensation pressure loss and the evaporation pressure loss are almostthe same. Regarding the pressure loss in a wide range of the refrigerantflow rate of 10 to 25 kg/h, no superiority or inferiority is observedamong them, and they have the same performance.

Therefore, excellent thermal conductivity can be obtained in the innerspiral grooved tubes according to Examples 1, 11 and 12 in a widerefrigerant flow rate range.

REFERENCE SIGNS LIST

-   -   1: heat exchanger    -   2: inner spiral grooved tube,    -   3: heat dissipating plate    -   6: tube body,    -   6 a: outer peripheral surface    -   6 b: inner peripheral surface    -   7: fin    -   7 a: tip part    -   7 b: bottom part    -   7 c: sidewall part    -   8: spiral groove    -   9: raw tube    -   9A: straight fin    -   9B: straight groove    -   A: manufacturing apparatus    -   14: fin    -   14 b: bottom part    -   14 c: sidewall part    -   16: spiral groove    -   a: fin top width    -   b: fin bottom width    -   c: fin spacing    -   h: fin height    -   θ: fin apex angle    -   11: unwound bobbin    -   17: first drawing dice    -   18: first guide capstan    -   19: second drawing dice    -   21: first revolving capstan    -   22: second revolving capstan    -   23: revolving flyer

1. An inner spiral grooved tube, comprising: a tube body; and aplurality of grooves and a plurality of fins aligned in an innercircumferential direction of the tube body, wherein the grooves and thefins are formed in a spiral along a longitudinal direction of the tubebody, an outer diameter of the tube body is 3 mm or more and 10 mm orless, a number of the fins formed on an inner peripheral surface of thetube body is 30 to 60, the inner spiral grooved tube is made of a metal,a cross sectional shape of each of the fins in a cross section of thetube body has a rectangular shape having an apex angle of 0±10°, a ratioh/f is 0.90 or more and 3.40 or less, h being a fin height and f beingfin width, a ratio c/f is 0.50 or more and 3.80 or less, c being a finspacing between adjacent fins in the inner circumferential direction ofthe tube body, and an average obtained by summing the ratio h/f and theratio c/f and dividing a sum in half is 0.8 or more and 3.3 or less. 2.The inner spiral grooved tube according to claim 1, wherein the fins arearranged with an equal spacing in the inner circumferential direction ofthe tube body.
 3. The inner spiral grooved tube according to claim 1,wherein the cross sectional shape of each of the fins in the crosssection of the tube body has a rectangular shape having an apex angle of0±10° and the average of the ratio h/f and the ratio c/f is 2.0 or moreand 2.8 or less.
 4. The inner spiral grooved tube according to claim 1,wherein the cross sectional shape of each of the fins has a rectangularshape having an apex angle of 0±5°, and the average of the ratio h/f andthe ratio c/f is 2.4 or more and 2.6 or less.
 5. The inner spiralgrooved tube according to claim 1, wherein the tube body is made ofaluminum or an aluminum alloy.
 6. A heat exchanger, comprising the innerspiral grooved tube according to claim 1.